ProgressIndicator.setProgress(double), if called from another thread than the FX application thread, and with a negative value as argument, throws the following exception:

Exception in thread "Thread-5" java.lang.IllegalStateException: Not on FX application thread; currentThread = Thread-5
at com.sun.javafx.tk.Toolkit.checkFxUserThread(Toolkit.java:237)
at com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(QuantumToolkit.java:397)
at javafx.scene.Parent$1.onProposedChange(Parent.java:245)
at com.sun.javafx.collections.VetoableObservableList.setAll(VetoableObservableList.java:90)
at com.sun.javafx.collections.ObservableListWrapper.setAll(ObservableListWrapper.java:314)
at com.sun.javafx.scene.control.skin.ProgressBarSkin.initialize(ProgressBarSkin.java:289)
at com.sun.javafx.scene.control.skin.ProgressBarSkin.access$400(ProgressBarSkin.java:56)
at com.sun.javafx.scene.control.skin.ProgressBarSkin$5.invalidated(ProgressBarSkin.java:210)
at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(ExpressionHelper.java:155)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:100)
at javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:197)
at javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl.access$100(ReadOnlyBooleanWrapper.java:167)
at javafx.beans.property.ReadOnlyBooleanWrapper.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:163)
at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:128)
at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:161)
at javafx.scene.control.ProgressIndicator.setIndeterminate(ProgressIndicator.java:110)
at javafx.scene.control.ProgressIndicator.access$200(ProgressIndicator.java:62)
at javafx.scene.control.ProgressIndicator$2.invalidated(ProgressIndicator.java:161)
at javafx.beans.property.DoublePropertyBase.markInvalid(DoublePropertyBase.java:129)
at javafx.beans.property.DoublePropertyBase.set(DoublePropertyBase.java:163)
at javafx.scene.control.ProgressIndicator.setProgress(ProgressIndicator.java:150)